The present invention relates to field devices of the type used to couple to industrial processes. More particularly, the present invention relates to controlling the temperature of such a field device.
Industrial processes are used in a wide variety of applications to produce various types of products. For example, an oil refinery includes numerous industrial processes which are used to refine crude oil into various usable products.
Typically, processes require both monitoring and controlling. For example, one type of field device is a transmitter which can be used to monitor process variables such as pressure, flow, temperature, etc. of the process. Based upon the measured process variable, another type of field device, a controller, is used to control process variables of the process. Various types of controllers are used to adjust flow rate, control temperature, control pressure, etc.
In some installations, it is desirable that the temperature of the field device be maintained at an elevated temperature. For example, in some ultra high purity process environments such as those used in semiconductor manufacturing, if the temperature of the field device drops below a melting point of a fluid in the process, the fluid will solidify and adhere to the field device. Additionally, if the field device is temperature sensitive, errors can be reduced by maintaining the temperature of the field device.
One technique which has been used to maintain the temperature of field devices is the use of heater elements which are coupled to the field device. The heater element can, for example, include an internal temperature sensor and thermostat for controlling the temperature of the heater element. Heaters are also used if the device is placed in a cold environment, for example, during winter, a heated jacket can be used to heat the transmitter and assorted piping. However, the heated jacket must be switched off during summer to prevent overheating.